# std::mbrtoc16

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< cpp‎ | string‎ | multibyte

Defined in header `<cuchar>` |  |
std::size_t mbrtoc16( char16_t* pc16, const char* s, std::size_t n, std::mbstate_t* ps ); |  | (since C++11)

Converts a narrow multibyte character to UTF-16 character representation.

If s is not a null pointer, inspects at most n bytes of the multibyte character string, beginning with the byte pointed to by s to determine the number of bytes necessary to complete the next multibyte character (including any shift sequences). If the function determines that the next multibyte character in s is complete and valid, converts it to the corresponding 16-bit character and stores it in *pc16 (if pc16 is not null).

If the multibyte character in *s corresponds to a multi-char16_t sequence (e.g. a surrogate pair in UTF-16), then after the first call to this function, *ps is updated in such a way that the next call to `mbrtoc16` will write out the additional char16_t, without considering *s.

If s is a null pointer, the values of n and pc16 are ignored and the call is equivalent to std::mbrtoc16(nullptr, "", 1, ps).

If the wide character produced is the null character, the conversion state *ps represents the initial shift state.

The multibyte encoding used by this function is specified by the currently active C locale.

### Parameters

pc16 | - | pointer to the location where the resulting 16-bit character will be written
s | - | pointer to the multibyte character string used as input
n | - | limit on the number of bytes in s that can be examined
ps | - | pointer to the conversion state object used when interpreting the multibyte string

### Return value

The first of the following that applies:

- ​0​ if the character converted from s (and stored in *pc16 if non-null) was the null character.
- the number of bytes [1...n] of the multibyte character successfully converted from s.
- -3 if the next char16_t from a multi-char16_t character (e.g. a surrogate pair) has now been written to *pc16. No bytes are processed from the input in this case.
- -2 if the next n bytes constitute an incomplete, but so far valid, multibyte character. Nothing is written to *pc16.
- -1 if encoding error occurs. Nothing is written to *pc16, the value EILSEQ is stored in errno and the value of *ps is unspecified.

### Example

Run this code

    #include <clocale>
    #include <cstring>
    #include <cuchar>
    #include <cwchar>
    #include <iomanip>
    #include <iostream>

    int main()
    {
        std::setlocale(LC_ALL, "en_US.utf8");

        std::string str = "z\u00df\u6c34\U0001F34C"; // or u8"zß水🍌"

        std::cout << "Processing " << str.size() << " bytes: [ " << std::showbase;
        for (unsigned char c: str)
            std::cout << std::hex << +c << ' ';
        std::cout << "]\n";

        std::mbstate_t state{}; // zero-initialized to initial state
        char16_t c16;
        const char* ptr = &str[0], *end = &str[0] + str.size();

        while (std::size_t rc = std::mbrtoc16(&c16, ptr, end - ptr + 1, &state))
        {
            std::cout << "Next UTF-16 char: " << std::hex
                      << static_cast<int>(c16) << " obtained from ";
            if (rc == (std::size_t)-3)
                std::cout << "earlier surrogate pair\n";
            else if (rc == (std::size_t) - 2)
                break;
            else if (rc == (std::size_t) - 1)
                break;
            else
            {
                std::cout << std::dec << rc << " bytes [ ";
                for (std::size_t n = 0; n < rc; ++n)
                    std::cout << std::hex << +static_cast<unsigned char>(ptr[n]) << ' ';
                std::cout << "]\n";
                ptr += rc;
            }
        }
    }

Output:

    Processing 10 bytes: [ 0x7a 0xc3 0x9f 0xe6 0xb0 0xb4 0xf0 0x9f 0x8d 0x8c ]
    Next UTF-16 char: 0x7a obtained from 1 bytes [ 0x7a ]
    Next UTF-16 char: 0xdf obtained from 2 bytes [ 0xc3 0x9f ]
    Next UTF-16 char: 0x6c34 obtained from 3 bytes [ 0xe6 0xb0 0xb4 ]
    Next UTF-16 char: 0xd83c obtained from 4 bytes [ 0xf0 0x9f 0x8d 0x8c ]
    Next UTF-16 char: 0xdf4c obtained from earlier surrogate pair

### See also

c16rtomb (C++11) | converts a UTF-16 character to narrow multibyte encoding (function)
mbrtoc8 (C++20) | converts a narrow multibyte character to UTF-8 encoding (function)
do_in [virtual] | converts a string from `ExternT` to `InternT`, such as when reading from file (virtual protected member function of `std::codecvt<InternT,ExternT,StateT>`)
C documentation for mbrtoc16

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